Valves are known for sacks or bags to be pressurised, for instance with air, the valve comprising a flange and a threaded connection. The screwed connection has to be detached from the flange, if the valve is to be opened and tightened if the bag or sack is to maintain the air pressure. The valve per se can be further secured by means of a separate plug. Such valve constructions known inter alia from Swedish published specification No. 425.233 and PCT publication No. WO 91/10598.